Ph (Mid To High Range) Ta (Real Low)

[Asfyxiate]

Hey guys,

I've looked around and can't really find a good solution to my problem.

I run 4 spas and 1 outdoor pool. For the most part the pH is 7.5-7.9. But the Alk can vary from 40-60ppm. We use cal-hypo in the pool and the 2 outdoor spas, and sodium hypochlorite in the 2 indoor spas. We use HCl to lower and sodium bicarbonate to raise.

Other info:

Make up water tends to have high numbers.

Automatic feeders and controllers (although I do use FAS-DPD)

TOR for the pool is 4 1/2 hrs.

TOR for the outdoor spas 30 mins

TOR for the indoor spas 20 mins.

CYA in the outdoor pool/spas - 20ppm

Pool temp 88F

Spas 102-104F

All bodies of water circulate 24hrs

Any advice, or ideas would be highly appreciated. Thanks.

*Sorry posted to the wrong thread*

Moved to Hot Tub Water Chemistry by Moderator

Edited May 14, 2011 by waterbear

[waterbear]

Actually, if you are using unstabilized chlorine sources (which you are) then your TA is not that low, recommened range is 80 to 100 ppm and lower often leads to better pH stability. All you need to do is raise the calcium hardness to keep the water balances and slow down the acid feed and you should find that the pH will stabilize around 7.6-7.8. It is highly unlikely that you will need to raise the pH given the chemicals you are using but you might need to raise TA from time to time since it will be depleted by the acid additions.

There are things you did not learn in the CPO course about water chemistry because they are just not taught and this post makes it evident

Some guidelines to help you. Don't lower the pH below 7.6 since this will slow the pH rise from outgassing of carbon dioxide (which will be the main source of your pH rise with unstabilized chlorine which has a net neutral pH (alkaline when applied, acidic on sanitzing so net effect on pH is close to 0)

Lower the pH when it hits 7.8 back to 7.6. If you are using acid feed pumps then adjust to maintain the pH at 7.6, if you are manually dosing be sure to do an acid demand test and measure the acid so you don't drop it too low.

Keep your TA at 80 ppm and not higher because this will also slow pH rise from outgassing of CO2. bump it up when it hits 60. In the pool (where there is less aeration) you can probably have the TA a bit higher, say 100 ppm, without much negative impact on pH stability.

Also, this post on how to lower TA contains some background chemistry that is not taught in CPO courses and might be helpful to you for a better understanding of the relationship between TA and pH.

Finally, this post in a different forum on carbonate alkalinity might be helpful to you.